We have used 25 sets of oligonucleotide primers specific for the 24 known major human T-cell receptor (TCR) V beta families in polymerase chain reactions to analyse the T-cell repertoire of the peripheral blood in seven patients with chronic myeloid leukaemia (CML). In contrast to normal healthy individuals, all seven patients exhibited variable degrees of TCR V beta-specific T-cell deletion, ranging from two to eight of the 24 major families. T cells bearing V beta 17 and 8 were most commonly deleted. These results suggest a superantigen effect associated with CML. The patterns of deletion did not appear to correlate with either of the two bcr-abl transcripts. The reason and aetiological agent responsible for the T-cell deletion remain speculative. Further work is ongoing to characterize this phenomenon in animal models and patients with CML.